This invention relates to the field of organometallic syntheses and to a process for forming organometallic cyclometallated complexes of transition metals comprising the step of reacting an organozinc complex of a desired organic ligand with a metal complex of an element bearing a leaving group to form the corresponding cyclometallated compound.
Organometallic cyclometallated complexes of third-row transition metals (e.g. iridium, platinum) have become useful materials and have necessitated synthetic methods for preparing them. Lamasky et al., Inorg. Chem., 2001, 40, 1704-1711, react a bis-cyclometallated iridium complex with excess amount ligand to form a tris complex. However, this method leads to a mixture of isomers in some cases. Tamayo et al., J. Am. Chem. Soc. 2003, 125, 7377-7387, reported an improved method to form a pure meridianal isomer of a tris iridium complex. However, the procedure is inconvenient and necessitates finding exact conditions for the reaction of each substrate and therefore is not generally applicable. Furthermore, an efficient and general method for the preparation of mixed tris-cyclometallated iridium complexes has not been developed yet. Grushin et al, U.S. 2002/0190250 A1, reported that the reaction of the trifluoroacetate intermediate of a bis-cyclometallated iridium complex, which was prepared in two steps, with a third ligand produced a meridianal mixed tris-cyclometallated iridium complex, however, no information on isomeric purity was given. A similar method involving the reaction of a bis-cyclometallated iridium compound with a third ligand in glycerol at 180xc2x0 C. was reported to give a mixed cyclometallated iridium complex (U.S. 2003/0068526 A1). However, we repeated the same reaction and found that a mixture of a series of homoleptic and heteroleptic tris-cyclometallated iridium complexes was formed.
Chassot et al., Inorg. Chem., 1984, 23, 4249-4253, have prepared cyclometallated complexes of platinum by reacting a lithiated ligand with trans-dichlorobis(diethylsulfide)platinum. Jolliet et al., Inorg. Chem., 1996, 35, 4883-4888, also used lithiated ligands to form cyclometallated complexes of the ligands with platinum or palladium, and Lamansky and Thompson, in International Patent Application WO 00/57676, used the same procedure for the preparation of cyclometallated transition metal complexes. These procedures suffer from low yields, as well as the relative instability of and difficulty in handling lithiated organic materials.
It is a problem to be solved to provide a process for the synthesis of organometallic cyclometallated complexes of transition metals that is convenient and generally applicable, is versatile, can be used with a variety of transition metals, and provides high yields, purity, and good control over isomer formation.
The invention provides a process for forming an organometallic cyclometallated complex comprising the step of reacting, in an aprotic organic solvent, an organozinc complex of a desired organic ligand with a metal complex of an element of atomic number 74 to 79 bearing a leaving group. The process forms the corresponding cyclometallated compound. The process is versatile and provides high yield and pure isomers of cyclometallated compounds of transition metals. It can be used to prepare complexes of mixed ligands, can be used with a variety of transition metals, and can utilize solvents that cannot be used with lithiated ligands.